DESCRIPTION: (Applicant's Abstract) Stimuli which raise intracellular cAMP levels are know to induce apoptosis in specific, susceptible lymphoid populations. cAMP metabolism is controlled by at least ten distinct families of cyclic nucleotide phosphodiesterases (PDEs). Recently, chronic lymphocytic leukemia (CLL) cells were shown to undergo apoptosis following exposure to the nonspecific PDE inhibitor theophylline. The applicant recently identified murine PDE4B as an enzyme upregulated during the induction of thymocyte apoptosis by in vivo administration of anti-CD-epsilon, and resolved to determine whether inhibition of PDE4 induced cAMP-mediated apoptosis in CLL. CLL cells contained PDE4B transcript, protein and enzymatic activity. Inhibition of PDE4 by rolipram raised cAMP levels and induced apoptosis in CLL cells in a dose dependent fashion that required 48 hours to achieve maximal effect. WMC and anti-Ig stimulated primary human B cells were resistant to rolipram-induced apoptosis. It is proposed to examine the hypothesis that lymphoid sensitivity to PDE inhibitor-induced apoptosis may in part be determined by physiologic and developmental regulation of PDE family expression or by malignant transformation. First, the expression of PDE1B, 3B, 4A, 4B, 4D and 7 enzymes will be examined in CLL, ALL, ATL and Sezary leukemic cells as well as B cells and immature and mature T lymphocytes using Western blot analysis, PCR, RNase protection, Northerns and enzyme assays. It will also be determined whether stimuli which activate normal and malignant B and T cells alter PDE family expression, followed by correlation of these studies with the ability of family-specific PDE inhibitors to induce apoptosis in these resting or activated normal and malignant cells. It will be determined whether family specific PDE inhibitors induce compensatory increases in other families of PDEs and whether inhibition of several families of PDEs is more effective in inducing apoptosis than "monotherapy." To investigate other mechanisms by which lymphoid populations differ in their sensitivity to cAMP-induced apoptosis, the following will be examined: 1) The role of the GTPase RAP1 in cAMP-mediated apoptotic signaling in lymphoid cells; 2) The role of cAKI and cAKII in cAMP-mediated apoptosis; 3) Whether the association of PKA and BAD S112 kinase activity with mitochondrial fractions in lymphoid cells predicts sensitivity to PDE inhibitor-induced apoptosis. The information gathered in this project will assist in the rational application of family-specific PDE inhibitors to the treatment of human lymphoid malignancies.